Xantia MK2 - Blower speed unstable

[lancia58]

Hi

The heating blower speed is unstable , when I put the fan speed knob at the off position it will continue to revolve slow though, when I move the know to the higher speed position the blower speed is unstable and sometimes it turns off.
When this happens ‘jiggle’ the knob causing the blower to revolve . Does this indicate that the Heater Blower Motor Transistors are faulty or the heater control panel is faulty to be more accurate the fan speed control slider electrical contacts are worn ?

Thanks
Zohar